so apperently i need a new cpu since my defroster doesnt work nor does my top go down and ! my horn dont work. i looking in the fsm and all of it is routed thru the cpu.

sooooo this leads me to my question.. how do i kno what cpu i need?
i have a 88 s4 vert

 

there is a number on it. get one with the same number.

 

oh.. and does my logic of thinking sound plausible?

 

Rear window defroster does not go thu the CPU on a series four. Convertibles have a rear window defroster?

Neither does the convertible top on a series four.

Horn does. That's one out of three.

 

Sounds like backwards logic to me

 

I'm assuming you have checked the fuses and wiring? I'd assume I had a bad connector somewhere in that line before the ecu.

ECU # N338 - according to https://www.rx7club.com/showthread.p...03#post9621203

Looks like you can pick one up on ebay for around $100.00 (might consider a rtek upgrade since you are replacing the ecu have it tuned for better mileage and/or power)

 

ECU's don't do the following.......................HORN.........CONVE RTIBLE TOP.........nor REAR WINDOW DEFROSTER.

CPU on series four don't do ...........CONVERTIBLE TOPS...........REAR WINDOW DEFROSTER. But do do HORNS.

 

Yes in fact they do....

 

The horn and brake lights share the same fuse ( 20 amp located in the battery bus), thus if the brake lights are operational then that rules out a blown fuse. There are basically "three" wires connected to the horn relay found on the horn circuit board. Green/White wire "always" has voltage on it. Green/Orange wire carries a ground signal when the horn button is depressed. Green/Red wire carries voltage to the "two" horns when the relay closes. This is supposed to occur when G/W has voltage and G/O has ground to it.

 

i thought there was stuff that went into the cpu that had to do with the top...
the reason why i dont think its the switch and stuff is cause everything was WORKing fine till i messed up one day and connected a battery wrong(plz dont flame..) i burnt up my logicon and stuff.

ill post a pic in a few ..
also how is my logic flawed? not trying to be an *** i just want to understand what exactly im doing wrong.

 

Uploaded with ImageShack.us see why i thought that the cpu had SOMETHIng to do with the cpu

 

there we go way better size..

im thinking that it might have something to do with the parking brake sensor..
im just trying to try everything possiable before i buy two new motors because i followed the fsm process tree..

 

The online wiring diagrams only show the HORN related to the CPU. The others have no connection to the CPU according to the online series four wiring diagrams.

BODY ELECTRICAL probably has a trouble shooting path for the convertible top and defroster.

Series five are different.

 

wait do i have the wrong fsm? because the pic you posted and the pic i have are different.. i got mine from http://www.cochran-racing.com/FSM/s4/index.html

 

Your right and I'm wrong. CPU is in the system according to the BODY ELECTRICAL. So much for the online wiring diagrams.

 

its cool we all human.
so i am thinking right? atleast for the top that is?

 

Anyway, the defroster is not CPU related. But there's something about the defrost relay in the rear of the car that is somewhat interesting.

It has one LARGE wire to that relay that is batt power to the relay. Large wire. So keeping this in mind...........if someone was going to run a seperate wire to the fuel pump to power it, why run a new wire from the engine bay when this large WHITE wire exists a half foot from the fuel pump plug? Just use it is what I'm saying. And that relay could be controlled by just eliminating the wire to the timer and just grounding that particular wire permanetly. So every time the key is put to ON, the relay pulls in and supplies power from the WHITE wire to the fuel pump.

Like you'd gnd the B/L wire permanetly...........WHITE would feed the B/W wire on the other side of the relay when the key is put to ON. And the B/W would go to the fuel pump feed wire.

WHITE is on a 30a breaker in the interior fuse box at the very top of that box.

Who needs a defrost anyway. I use the B/G wire on that defrost relay to power my boat trailer lights.

 

if you want your cpu fixed there are cold soilder joints that always crack kinda suprised hilers hasnt said anything its really simple to do takes less then 30mins and saves you a few bux